1. Field of Invention
This invention relates to a diagnostic apparatus employing nuclear magnetic resonance (NMR), and more particularly, to means for preventing the image quality from being degraded due to time dependent variations of the primary magnetic field intensity in an NMR computerized tomographic apparatus.
2. Description of the Prior Art
Conventional NMR diagnostic apparatus, such as NMR computerized tomographic apparatus, generate a primary magnetic field by energizing a primary magnetic field coil with a constant current. However, the power supply for the primary magnetic field coil may vary in its output, or the primary magnetic field coil may vary in its shape due to variations in the room temperature or the temperature of the primary magnetic field coil per se, with the result that the intensity of the primary magnetic field may vary over a few tens ppm. When the primary magnetic field varies in intensity, the image of a diagnosed area is liable to suffer from an artifact.